The auto play limitation in mobile browsers is an intentional limitation put in by the OS developers. To my knowledge, there is absolutely no way to auto play content in a mobile browser because the event that is required to trigger content play is an OS/Phone event, one which the browser itself has no control over or interaction with.

Facebook has implemented a video auto play feature to its advertising arsenal, but this is only through its native app. Even the mighty FB must surrender its will to the power of the phone gods.

I found one article about this new FB ad presentation technique that had some users in the comments section complaining about a way to disable autoplay in browsers like you can with the native FB app: